Published in BMC Chemistry in September 2026, the study introduces a polyvinylidene fluoride (PVDF) membrane modified with a specific metal-organic framework hybrid, designated as ZIF-8@g-C3N4 or ZGCN. The primary objective of this work was to overcome the limitations of traditional PVDF membranes, which often suffer from low permeability, significant fouling, and a trade-off between water flux and separation efficiency. By integrating the ZGCN nanohybrid directly into the membrane matrix, the team aimed to enhance both the physical structure and the chemical surface properties of the filtration material.

The synthesis of the ZGCN nanohybrid involved a two-step process that combined the distinct advantages of two different materials. First, graphitic carbon nitride (g-C3N4) was prepared through the thermal condensation of melamine at 550 degrees Celsius. Subsequently, zeolitic imidazolate framework-8 (ZIF-8) nanocrystals were grown in situ on the surface of the g-C3N4 sheets under solvothermal conditions. This hybrid approach leverages the high porosity and molecular sieving capabilities of ZIF-8 alongside the hydrophilic and photocatalytic properties of g-C3N4. The resulting nanoparticles were then dispersed in a PVDF casting solution to form the composite membrane via the phase inversion method.

Comprehensive characterization techniques confirmed the successful integration of the nanohybrid into the polymer matrix. X-ray diffraction analysis revealed that both the ZIF-8 and g-C3N4 phases retained their crystalline structures within the composite, indicating that the hybridization process did not compromise the individual functionalities of the materials. Brunauer-Emmett-Teller surface area analysis showed that the ZGCN nanohybrid achieved a surface area of 987 square meters per gram, significantly higher than pure g-C3N4. This high porosity, combined with a mesoporous structure identified through nitrogen adsorption-desorption isotherms, provides numerous interaction sites for organic molecules, which is critical for effective filtration.

The physical morphology of the modified membranes was examined using scanning electron microscopy. The images displayed a well-dispersed ZGCN phase within the PVDF matrix, resulting in a more open and porous structure compared to the pristine membrane. The presence of the nanohybrid promoted the formation of macrovoids during the phase inversion process, a phenomenon attributed to the nucleation effect of the nanoparticles. This enhanced pore structure is directly linked to the improved water permeability observed in the modified membranes, as the increased porosity reduces hydraulic resistance and facilitates faster water transport through the membrane.

Surface hydrophilicity was a key factor in the performance enhancement, as measured by water contact angle tests. The pristine PVDF membrane exhibited a contact angle of 87.6 degrees, reflecting its inherent hydrophobic nature. In contrast, the ZGCN-modified membrane showed a significantly lower contact angle of 62.3 degrees. This marked increase in hydrophilicity is attributed to the polar functional groups present in the g-C3N4 component, which improve water affinity. A more hydrophilic surface not only allows for higher water flux but also reduces the adhesion of organic foulants, thereby mitigating the fouling process that typically degrades membrane performance over time.

The filtration performance of the membranes was evaluated using a synthetic humic acid solution at a concentration of 20 mg/L and a constant transmembrane pressure of 2 bar. The ZGCN-PVDF membrane demonstrated an initial pure water flux of 318.5 liters per square meter per hour, which is substantially higher than the 201.3 liters per square meter per hour recorded for the pristine PVDF membrane. After four hours of continuous filtration, the flux of the modified membrane stabilized at 172.8 liters per square meter per hour, whereas the pristine membrane’s flux dropped sharply to 110.7 liters per square meter per hour. This sustained flux indicates that the modified membrane maintains its permeability more effectively during operation, a crucial attribute for long-term water treatment applications.

In addition to higher flux, the modified membrane achieved superior rejection of humic acid. The average rejection efficiency for the ZGCN-PVDF membrane was 91.6%, compared to only 76.4% for the pristine PVDF membrane. This improvement is attributed to the dual mechanism of physical sieving by the ZIF-8 framework and electrostatic interactions between the negatively charged humic acid molecules and the ZGCN-functionalized surface. The polar nitrogen-containing groups in g-C3N4 also contribute to stronger adsorption interactions, further enhancing the membrane’s ability to retain organic contaminants. Statistical analysis confirmed that these improvements were significant, with one-way ANOVA tests showing a highly significant difference in rejection efficiency between the two membrane types.

Antifouling performance was assessed by measuring the flux recovery ratio after a physical rinsing step with deionized water. The pristine PVDF membrane exhibited a flux recovery ratio of only 63.4%, indicating severe irreversible fouling. In contrast, the ZGCN-PVDF membrane demonstrated a significantly improved ratio of 89.2%. This enhanced antifouling behavior is linked to the increased surface hydrophilicity and the potential photocatalytic activity of g-C3N4 under ambient light, which may aid in the degradation of adsorbed foulants. The Hermia fouling model analysis identified intermediate blocking as the dominant fouling mechanism for both membranes, but the modified membrane showed a slower fouling rate, confirming the beneficial effect of ZGCN incorporation in mitigating pore blockage.

The study acknowledges that the use of a standardized humic acid sodium salt serves as a model foulant for controlled comparison with existing literature. While this approach allows for reproducible results, it does not fully capture the complexity of natural organic matter found in environmental waters. The authors note that future research should extend to environmentally relevant sources, such as IHSS Suwannee River reference materials, to provide a more comprehensive assessment of membrane performance under realistic conditions. Additionally, further investigation into long-term stability under continuous-flow conditions and scale-up of fabrication processes is recommended to evaluate the practical viability of this technology.

This research highlights the potential of combining metal-organic frameworks with carbon nitride materials to create high-performance membranes for water purification. The synergistic effects of the ZGCN nanohybrid address multiple performance bottlenecks simultaneously, including permeability, selectivity, and fouling resistance. By offering a promising pathway for sustainable water treatment, this work contributes to the broader effort to develop efficient and durable technologies for removing natural organic matter from water supplies. The findings suggest that tailored nanocomposite membranes can significantly enhance the efficiency of ultrafiltration processes, making them a viable option for addressing global water quality challenges.

The research was published in BMC Chemistry in September 2026, specifically in Volume 20, article number 195. The authors positioned their work within the broader context of water treatment challenges, noting that humic acid is a significant component of natural organic matter that can form carcinogenic disinfection byproducts and cause membrane fouling. Traditional treatment methods such as coagulation-flocculation and activated carbon adsorption often face limitations including high operating costs and the generation of secondary waste. The authors highlighted that while metal-organic frameworks have been used to modify membranes, previous studies often focused on single functional fillers or specific membrane functions, such as photocatalytic degradation, rather than direct incorporation of a preformed hybrid for humic acid separation.

The novelty of this specific approach lies in the direct blending of the preformed ZIF-8@g-C3N4 nanohybrid into the PVDF casting solution, rather than applying it as a surface coating or deposition after membrane formation. The authors noted that while other MOF/g-C3N4 systems have been integrated with PVDF membranes, those studies typically employed surface-deposition or heterojunction-coating approaches. By using non-solvent-induced phase separation with the hybrid already dispersed in the solution, the researchers aimed to achieve a uniform distribution of active sites throughout the membrane matrix. This method was intended to prevent nanoparticle agglomeration and maintain the mechanical integrity of the membrane, ensuring that the structural benefits of the hybrid were preserved during the fabrication process.

Statistical modeling was applied to quantitatively assess the membrane performance, providing a deeper understanding of the fouling mechanisms beyond simple flux measurements. The researchers utilized an exponential decay model to describe the flux decline over time, which provided an excellent fit for both the pristine and modified membranes. For the ZGCN-PVDF membrane, the model indicated an initial flux of 332.7 LMH with a fouling rate constant of 0.157 h⁻¹, demonstrating a strong correlation with the experimental data. Additionally, the Hermia fouling models were used to identify the dominant fouling mechanism, with the intermediate blocking model showing the highest correlation coefficients for both membrane types. This suggests that the fouling process was primarily driven by partial pore blockage and gradual constriction, rather than the formation of a thick cake layer or complete pore occlusion.

The kinetic modeling of rejection efficiency further supported the effectiveness of the modified membrane. Using a pseudo-second-order model, the researchers calculated the equilibrium rejection capacity for the ZGCN-PVDF membrane to be 91.0%, with a rate constant of 0.0048 min⁻¹. This indicated that the rejection of humic acid followed chemisorption-controlled kinetics, where surface interactions played a dominant role in the separation process. Statistical significance was confirmed through one-way ANOVA tests, which showed that the improvements in both flux and rejection efficiency were not due to experimental variability but were robust effects of the ZGCN incorporation.

The authors also compared their results with recently reported PVDF/MOF-based membranes to contextualize the performance of their new material. The ZGCN-PVDF membrane exhibited a water flux of 318.5 LMH, which exceeded the fluxes of other reported membranes such as PVDF/Ag@MOF-0.5 and PVDF/MOF-199. While some other membranes achieved higher rejection or flux recovery ratios, the ZGCN-PVDF membrane offered a competitive balance of permeability, separation efficiency, and antifouling performance at a relatively low operating pressure of 2 bar. This comparison underscores the potential of the ZGCN nanohybrid as a versatile additive for enhancing PVDF membranes in water treatment applications, particularly for the removal of humic acid from water supplies.

Subject of Research: Development of ZIF-8@g-C3N4 modified PVDF ultrafiltration membranes for humic acid removal

Article Title: High-performance PVDF ultrafiltration membranes modified with ZIF-8@g-C₃N₄ nanohybrids for enhanced humic acid removal and antifouling performance

Article References: El-Sawaf, A. K., Nassar, A. A., Taha, A., & Mubarak, M. F. (2026). High-performance PVDF ultrafiltration membranes modified with ZIF-8@g-C₃N₄ nanohybrids for enhanced humic acid removal and antifouling performance. BMC Chemistry, 20(1), Article 195. https://doi.org/10.1186/s13065-026-01932-9

Image Credits: AI Generated

DOI: 10.1186/s13065-026-01932-9

Keywords: PVDF membranes, ZIF-8, g-C3N4, Ultrafiltration, Humic acid, Antifouling, Water treatment, Nanohybrids, Membrane filtration, BMC Chemistry, High-performance, PVDF